In order to measure a specific component in a liquid sample quickly and simply, for example, glucose, cholesterol or the like in a blood sample, or glucose, hemoglobin or the like in a body fluid sample, a dry type test apparatus comprises a support having thereon a reagent layer containing at least a reagent capable of developing a color by a reaction with the specific component.
When the test apparatus is used, the reaction starts by the supply of a liquid sample to one side of the reagent layer.
A color density of the developed color on the reagent layer after the reaction with a specific component corresponds to the amount of the specific component in the liquid sample. Accordingly, the specific component in the liquid sample can be determined by measuring the color density. The color density of the developed color on the reagent layer is measured by applying an incident light to the reagent layer after the color reaction and detecting intensity of the resulting reflected light or transmitted light.
Test apparatuses using reflected light can be divided roughly into two types from the viewpoint of sample supply to the reagent layer; one is a test apparatus having a sample-supplying area and a detecting area (namely, an incident light side area) on the same side, and another is a test apparatus having a sample-supplying area and a detecting area on different sides.
The test apparatus having a sample-supplying area and a detecting area on the same side is useful in measuring samples having high transparency such as sera and urine, but not suitable for measuring having low transparency such as whole blood.
On the other hand, the test apparatus having a sample-supplying area and a detecting area on different sides is markedly advantageous, because it is fully possible to measure a sample having low transparency such as whole blood by forming a reflection layer or a separation layer on the reagent layer.
In the test apparatus having a sample-supplying area and a detecting area on different sides, however, not only the reagent layer but also the structure of the test apparatus itself become complex in comparison with the test apparatus having a sample-supplying area and a detecting area on the same side. Accordingly, new components are often required in addition to the reagent layer and support. Examples of the test apparatus having a sample-supplying side and a detecting side on different sides include those which are disclosed in JP-A-55-59326 and JP-A-4-188065 (the term "JP-A" as used herein means an "unexamined published Japanese patent application").
The reflection layer is provided in order to clarify a coloring degree of the reagent layer by reflecting the injected light, and white particles of titanium dioxide or the like are used as its material. The usually used reflection layer has a thickness of from 2 .mu.m to 50 .mu.m. Also, light reflection capacity is added to the reagent layer itself by kneading titanium dioxide with a reagent in the reagent layer.
However, the reflection layer has a disadvantage in that it cannot perform complete reflection of light so that the light partially passes through the layer. When the thickness of the light reflection layer is increased in order to prevent such an unnecessary passage of light, the permeability of the liquid sample becomes poor so that proper results cannot be obtained.
In the case of the test apparatus of JP-A-4-188065, the portion corresponding to the reagent layer, as shown in FIG. 2 in expanded view, comprises a porous membrane to be used as a sample-holding layer, a reagent layer prepared from a reagent, a buffer, a binder and the like, a light reflection layer prepared from titanium dioxide which also acts as a blood cell filtration layer, a space where the supplied liquid sample passes, and a cover which forms a space above the reagent layer.
When light is injected into the reagent layer from the porous membrane side, types of the resulting reflected light are divided roughly into (1) light reflected from the porous membrane surface, (2) light reflected from the inner portion of the porous membrane and the inner portion of the reagent layer, (3) light reflected from the light reflection layer and (4) light reflected from the cover. Although necessary information among them is only the reflected light of (2) and (3), other types of reflected light are also measured. That is, the reflected light obtained by the injection of light is a mixture of several types of reflected light, and these unnecessary types of reflected light are generally measured as an error.
Even in the case of the same type of liquid sample such as whole blood, hemolytic serum, chromaturia or the like, the liquid sample itself sometimes shows different colors. For example, the color of whole blood varies depending on the difference in its hematocrit value and the like, and the color of serum varies depending on the difference in its degree of hemolysis and the like. Depending on the difference in the color of these liquid samples, coloration of the reagent layer varies and the amount of light passing through the reagent layer also varies.
When the measurement is carried out using reflected light, the light reflected from the cover provided on the side which is not the incident direction of the reagent layer (the aforementioned type (4) reflected light) is also simultaneously detected by its passage through the reagent layer, so that difference in the coloration of the reagent layer in each measurement causes changes in the amount of light which passes through the reagent layer and also the amount of the reflected light of type (4) which passed through the same, thus inevitably exerting unnecessary influence upon the measured values.